Mounting enclosure for burners and particle injectors on an electric arc furnace

ABSTRACT

An enclosure for mounting burners and particle injection equipment in an EAF is described. The enclosures are mounted on the sidewalls of an EAF and include passages in which burners or injectors are mounted so that the discharge ends of the burners and injectors are located closer the melt than sidewall mounted burners and injectors. Burners and injectors mounted in the enclosures heat material in the furnace and deliver particulates to the melt more efficiently than conventionally mounted burners and injectors. The enclosures are liquid-cooled, typically by water, and constructed of high conductivity materials such as copper and/or cast iron and can be constructed in one or more pieces. Therefore, the enclosures protect the burners and injectors from the excessive heat and mechanical impact to which they would normally be subjected when mounted so close to the melt.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/011,557filed Oct. 30, 2001, which is a continuation-in-part of application Ser.No. 09/875,153 filed Jun. 6, 2001, now U.S. Pat. No. 6,749,661, which isa continuation-in-part of application Ser. No. 09/502,064 filed Feb. 10,2000, now U.S. Pat. No. 6,289,035, and a continuation-in-part ofapplication Ser. No. 09/902,139 filed Jul. 10, 2001, now U.S. Pat. No.6,614,831, which is a continuation-in-part of application Ser. No.09/502,064 filed Feb. 10, 2000, now U.S. Pat. No. 6,289,035. Thedisclosures of application Ser. Nos. 09/875,153; 09/902,139 and09/502,064 are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention generally relates to a method and apparatus usedin metal melting, refining and processing, for example, steel making inan electric arc furnace (EAF), and more particularly, to a method andapparatus for the introduction of chemical energy and particulates, forexample, carbon particles entrained in a carrier gas, in an EAF.

Electric arc furnaces (EAFs) make steel by using an electric arc to meltone or more charges of scrap metal which is placed within the furnace.Modern EAFs may also make steel by melting DRI (direct reduced iron)combined with the hot metal from a blast furnace. In addition to theelectrical energy of the arc, chemical energy is provided by auxiliaryburners using fuel and an oxidizing gas to produce combustion productswith a high heat content to assist the arc.

If the EAF is used a scrap melter, the scrap burden is charged bydumping it into the furnace through the roof opening from buckets whichalso may include charged carbon and slag forming materials. A similarcharging method using a ladle for the hot metal from a blast furnace maybe used along with injection of the DRI by a lance to produce theburden.

In the melting phase, the electric arc and burners melt the burden intoa molten pool of metal, termed an iron carbon melt, which accumulates atthe bottom or hearth of the furnace. Typically, after a flat bath hasbeen formed by melting of all the burden introduced, the electric arcfurnace enters a refining and/or decarburization phase. In this phase,the metal continues to be heated by the arc until the slag formingmaterials combine with impurities in the iron carbon melt and rise tothe surface as slag. During the heating of iron carbon melt it reachesthe temperature and conditions when carbon in the melt combines withoxygen present in the bath to form carbon monoxide bubbles which iscommonly termed as “carbon boil.” Generally, flows of oxygen are blowninto the bath with either lances or burner/lances to produce adecarburization of the bath by the oxidation of the carbon contained inthe bath.

The resulting decarburization reduces the carbon content of the bath toa selected level. If an iron carbon melt is under 2% carbon it becomessteel. Except for operations using the hot metal from the Blastfurnaces, the EAF steel making processes typically begin with burdenshaving less than 1% carbon. The carbon in the steel bath is continuallyreduced until it reaches the content desired for producing a specificgrade of steel, down to less than 0.1% for low carbon steels.

With the imperative to decrease steel production times in electric arcfurnaces, it becomes necessary to deliver effective decarburizing oxygento the iron carbon melt as early in the steel making process aspossible. Conventional burners mounted on the water cooled side walls ofthe furnace generally must wait until the melting phase of the processis substantially complete before starting high velocity injection ofoxygen for the decarburization process. These burners can not delivereffective high velocity oxygen to the bath early in to the melting cyclebecause unmelted scrap is in the way of the injection path and woulddeflect the oxygen flow. The bottom of the electric arc furnace isspherical shaped and the melted scrap forms the melt in the middle ofthe furnace first and then it rises filling up the sides.

Therefore, it would be highly advantageous to reduce the melting phaseof an electric arc furnace so that high velocity oxygen and carbon couldbe injected sooner and decarburize the melt faster.

One way to shorten the melting phase is to add substantially more energywith the burners at early times in the melting phase to melt the scrapfaster. There are, however, practical considerations with conventionalside wall mounted burners that limit the amount of energy which can beintroduced into the furnace and the rate at which it can be usedefficiently. The location of a conventional burners is subject toflashback. When scrap is initially loaded into the furnace, because itis located very near the flame face and oxygen jet of the burner, thedanger of a flash back of the flame against the side wall where theburner is mounted is significant. The panels where the burners aremounted are typically water cooled and a bum through of a water carryingelement in an electric arc furnace is a safety concern, as well as aproduction loss. To alleviate this concern, many fixed burners are runat less than rated capacity until the scrap is melted some distance awayfrom the face of the burner. Only after the burner face has been cleareddoes the burner operate to deliver its maximum energy.

Another problem to increasing the energy added during the early part ofthe melting phase is that the flame of the burner is initially directedto a small localized area of the scrap on the outside of the scrapburden. It is difficult to transfer large amounts of energy from theburner by this localized impingement to the rest of the scrapefficiently. Until the burner has melted the scrap away from its faceand has opened a larger heat transfer area, increasing a burner tomaximum output would result in overheating and melting scrap piecestogether producing the problems for the next stage of the EAF operation.

Therefore, it would be advantageous to be able to increase the amount ofenergy applied by a burner during the early part of the melting phasewhich did not produce a risk of flash back for the water cooled panelsof the upper shell of the furnace. It would also be advantageous to usethis increased amount of energy more efficiently and to transferincreased portions of the energy to the scrap burden without scrapagglomeration.

Conventionally, oxygen is blown or injected into the iron carbon meltwhere it reacts with the carbon in the molten bath to lower the carboncontent to the level desired for the end product. In general, the rateof decarburization in an electric arc furnace is determined by thecarbon concentration of the iron carbon melt, the oxygen injection rateand the surface area of the reactions sites. At higher bath carbonconcentrations, the reaction rate is not significantly limited by theavailability of carbon to enter the reaction. However, as the bathcarbon decreases to concentrations under approximately 0.15%-0.20% ofcarbon, it becomes increasingly difficult to achieve an acceptable rate.This is because the carbon concentration of the bath becomes thedecarburization rate determining factor. The decarburization rate, afterthe critical carbon content has been reached, is dominated by masstransfer of the carbon and the carbon concentration.

The prior art practice to decarburize an iron carbon melt ischaracterized by the localized application of a large volume of oxygenby means of devices such as lances and burner/lances. Due to thelocalized nature of this process, the decarburization rate depends onthe rate of oxygen injection to the bath, the carbon concentration andthe mass transfer of carbon to the reaction area. At lower carbon levelcontents, the iron oxide concentration in the slag near to the oxygenintroduction area reaches levels greater than equilibrium would allow,due to depleted local carbon concentration and poor mass transport. Thiscauses greater refractory erosion, loss of iron yield, increasedrequirements for alloys, and a low efficiency of oxygen utilization.

Therefore, it would be advantageous to provide a method and apparatus tosupply oxygen for efficient decarburization of the iron carbon melt atall carbon concentrations. A method that increased the number ofreaction zones and supplied significantly more effective oxygen early inthe process would be advantageous because it would shorten the durationof decarburization. Particularly important is the efficiency of theoxygen supply after the iron carbon melt reaches a low carbon content inorder to maximize the decarburization rate, without over oxidizing theslag and producing excess amounts of FeO. This would reduce operatingcosts by improving oxygen efficiency, reducing excess iron oxidation,improving alloy recovery, and increasing productivity.

The conventional oxygen injection equipment that has been used fordecarburization is not generally suited for efficient introduction ofoxygen into an iron carbon melt. The use of retractable consumable orwater cooled lances through the slag door opening, or through the sidewall, is always limited by the space available to position the equipmentaround the furnace, Its location is usually only practical in thequadrant of the furnace shell near the slag door. The basic furnacedesign, required manipulator movement, the size of the manipulator andthe necessity of operators to observe the manipulator operation dictatethe location of the manipulator. The design is also responsible for theintroduction of a substantial amount of cold ambient air into theprocess through the slag door or side wall opening during manipulationof the moveable lance. These large amounts of cold air reduce theefficiency of the process and also contribute to a nitrous oxideincrease in the furnace atmosphere. There is also a significant delay inmoving the lance into the furnace through the scrap burden. The scrapmust be melted in front of the lance before it can advanced into the hotreaction zone of the furnace where it can deliver effective oxygen.

Fixed oxygen injection equipment such as a burner/lance mounted on theside wall water cooled panels, or upper shells of the furnace arepositioned a significant distance away from the iron carbon melt. Thatdistance is generally determined by the geometry of the furnace sidewall with respect to the transition from the upper shell to the lowershell of the furnace which forms a step. The water cooled part of theupper shell where the burner/lances have been located is mounted on thelower shell or refractory, but typically about 15-24 inches back fromthe hot face of the refractory. Because a fixed burner/lance has had tofire over this step, the traditional fixed wall oxygen injectionequipment had to be located about 45 inches above the molten bath in anattempt to deliver oxygen with the optimum angle of impingement. Thisdistance and the angle requires the length of the injected stream ofoxygen to be about 65 inches or longer.

It is very difficult to deliver 1000 of an oxygen stream effectively toa reaction zone at these distances. The amount of effective delivery ofa high velocity (high kinetic energy) oxygen stream to the iron carbonmelt is proportional to the area of the oxygen injector opening (in thecase of a converging-diverging nozzle the area of the nozzle's throat)and the distance the oxygen jet travels to the iron carbon melt. Thus,increasing the area of the nozzle throat increases the total amount ofeffective oxygen reaching the iron carbon melt, but may also result inan increase of unused oxygen in the furnace atmosphere. Another methodof enhancing the effectiveness of an oxygen stream for decarburizationhas been to shroud it with the products of combustion, or other gases.The shrouding tends to maintain the stream together over a longerdistance thereby increasing its penetrating power. In spite of theeffectiveness gained by shrouding, it still has the limitation of howfar the gases can travel without significant energy loss. Locating theoxygen injection device far from the melt results in a significantamount of the oxygen being lost to the furnace environment and causingseveral detrimental effects on operations. Initially, there is theincreased cost of the shrouding gases and specialized equipment to formthe shroud. The excess oxygen causes damage to the side wall panels,erosion of the shell refractory, development of excessive iron oxide inthe slag, excessive electrode oxidation, reduction in the delta life,and may cause over heating of the furnace evacuation system.

Moreover, conventional oxygen injection equipment that has been used fordecarburization is not generally suited to varying the oxygen supplyrate over substantial ranges. Fixed oxygen injection equipment such asburner/lances mounted on the side wall panels of the furnace have theproblem that they are positioned some distance away from the surface ofthe iron carbon melt. These fixed lances obtain their oxygen injectioncapability by a supersonic or high velocity nozzle which accelerates theoxygen such that its kinetic energy is enough to penetrate the surfaceof the iron carbon melt even from considerable distances. If the flowrates of these injectors are reduced significantly, the high velocitynozzles will not impart enough gas velocity to the oxygen to penetrateand create an efficient reaction zone for decarburization.

The introduction of particulates in EAFs has also increased with therequirements for the efficient processing of iron carbon melts and areusually introduced for slag production. The production of a correct slagcomposition for the iron carbon melt during the refining phase isimportant in achieving desired steel chemistry and in cleaning the steelof impurities. Foamy slag practice where the slag entrains gas bubbles,usually CO gas bubbles, and expands in volume to cover the electrodes)of the furnace and protect furnace components from the arc radiation isvery desirable. Particulates, such as CaO and MgO, have been introducedto form slag and correct its chemistry to provide a good basis for slagfoaming. Slag foaming is generally accomplished by the introduction ofparticulate carbon into the bath where it reduces FeO to Fe in anendothermic reaction producing CO bubbles which expand the volume of theslag and cause it to foam. The foamed slag acts as a blanket to hold inheat for the process and to shield furnace components from the radiationof the electric arc.

Also particulate carbon has been introduced into the EAF environment forthe chemical adjustment of the carbon content an iron carbon melt.Normally, carbon is added to a melt for cleaning purposes or to increasethe carbon content if the carbon content of the original iron burdenmelted had been too low for the grade of steel desired.

Carbon has also been added to a slag which has high percentage of FeO torecover Fe from the slag to increase the yield of the steel. U.S. Pat.No. 4,362,556 issued to Kashida describes the process of recovering Fefrom the slag by reducing it with introduced particulate carbon. Thecarbon introduction is disclosed as being lanced with a pipe, either byitself or simultaneously with the introduction of oxygen.

Carbon has in the past been introduced into the EAF by a number ofmethods including adding it to the buckets of scrap which are beingmelted or by shoveling it through openings in the EAF, including ones inthe roof, sidewalls and the slag door. This has proved inefficient andother methods, such as moveable lances and fixed multimode burners, arenow used. U.S. Pat. 5,599,375 issued to Gitman, et al. illustrates amultimode burner which injects a simultaneous mixture of oxygen andparticulate carbon in an EAF. U.S. Pat. No. 4,986,847 issued to Knappdiscloses a slag door manipulator which simultaneously intersectsstreams of oxygen and carbon before injection into the furnace.

The incorporated Shver applications disclose a furnace apparatusmounting configuration which allows a multimode burner/lance to be movedcloser to the step of the furnace. The mounting enclosure andburner/lance configuration moves the burner flame away from the sidewallpanel to eliminate the chance for flashback and water cooled paneldamage. A more aggressive oxygen lancing practice can be used withoutrisk of damaging the sidewall panel and a more optimal oxygenconsumption can be achieved.

Similarly to the conventional burner/lance mounting configuration, acarbon injection stream is required to travel the same large distancethat a conventional oxygen jet must travel. Often the suction of thedirect evacuation system is strong enough to disrupt the carbon streamas it travels from the sidewall to the melt and thereby reduces theeffectiveness of slag foaming. The large distance which the conventionalcarbon injection stream must travel also reduces the velocity and energywith which it may penetrate the slag. Slag foaming is much moreeffective when the carbon stream can produce an intense agitation of theslag at its place of introduction.

Therefore, it would be advantageous to provide a particulate injectionprocess for EAF steelmaking, especially particulate carbon, which willintroduce the particulates low in the furnace and close to theslag/metal interface. The introduction of particulates in this mannerwill maximize the kinetic energy of the stream for penetrating andagitating the slag. It would also be advantageous for the particulateinjection to be accompanied by the injection of burner flames anddecarburizing oxygen low in the furnace and close to the slag metalinterface.

Prior art lances or burner/lances which simultaneously inject oxygen andcarbon have the problem of being located far from the melt and otherdrawbacks. The oxygen and carbon are generally mixed at the end of twonozzles by intersecting the flows far away from the iron carbon melt.Because the intersection angle is fixed at the time of mounting, theseconventional carbon and oxygen injection apparatus are only aligned oraimed to be effective when the iron carbon melt is at one level. Thislevel is usually chosen as the designed flat bath or fully melted levelof the furnace. However, no furnace actually operates at that level asmost are either overloaded or under-loaded to some degree in day to dayoperation. The designed level even changes as the refractory of thefurnace wears being higher at the start of a refractory regime and lowerat the end. Further, before a full scrap burden level is reached innormal EAF operation, several scrap buckets must go through the meltingcycle and it is not until the last bucket is entirely melted that thefull level of the furnace is even approached. Other conventional steelmaking processes have variable level baths, such as melting directreduced iron (DRI), or a ConSteel process. Therefore, these simultaneouscarbon and oxygen injection systems are not very efficient over much ofthe scrap melting steel making process and almost ineffective for manyother conventional steel making processes.

Therefore, it would be of advantage to provide a particulate injectionprocess for EAF steel making where the flows of oxygen and carbon weresubstantially parallel to each other and did not intersect. Asubstantially parallel introduction of each stream low in the furnaceand close to the slag/metal interface would provide effectivedecarburization and effective slag foaming to begin early in the processand at low bath levels. Further, the introduction of flows which did notintersect also would be effective over a wide range of bath levels.

Another drawback of the simultaneous oxygen and carbon systems whichintersect the flows is the use of the carbon as a fuel and not formetallurgical purposes. This drawback increases the farther away theyare introduced from the melt and their misalignment. The most efficientuse of supersonic oxygen is to decarburize the melt and the mostefficient use of carbon injection is to foam the slag and reduce the FeOin the slag. When mixed externally from the melt and slag, the oxygenand carbon combine to produce a flame leaving less of these elements fortheir intended uses. Further, their combined presence in one reactionzone slows the principle reactions desired (the decarburization of Feand the reduction of FeO) as they are more reactive with each other thanwith their intended metallurgical combinations. The exothermic reactionof the carbon and oxygen merely produces an insignificant amount ofuncontrollable heat while reducing the efficiency of and slowing themore desired processes.

Therefore, it would be advantageous to provide a particulate injectionprocess for an EAF in which the reaction zone for decarburization is inclose proximity to, but separate from the reaction zone for thereduction of FeO. This will maximize the primary reaction for thecarbon, while at the same time ensuring efficient FeO reduction andmaximum slag foaming. It would also be advantageous, however, if the twozones worked effectively together where the FeO produced by thedecarburization zone was actively reduced in the particulate reactionzone.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method and apparatus for improving theinjection of particulates in furnaces used for metal melting, refiningand processing. Preferably, the method and apparatus are useful forinjecting particulate carbon in the steel making operation of anelectric arc furnace. The particulate injection is advantageouslyaccomplished either alone, or in combination with the injection of oneor more other flows, such as a flame comprised of combustion products ora flow of oxidizing gas for decarburization.

According to one aspect of the invention used in a steel making processin an electric arc furnace, the duration of the process is decreased byadding increased amounts of chemical energy early in the process withthe combustion products of a burner/lance flame which is directed into amore efficient combustion reaction zone, preferably below the refractoryline of the furnace. When the burner flame is generated at this positionof the furnace, several distinct advantages pertain to a steel makingprocess. For a scrap melting process, the clearing of a path for aninjection of high velocity oxygen and particulates is facilitatedbecause there is less path length to clear and it can be done fester.The time for melting the path length is further reduced by increasingthe burner output to its maximum rating early in the melting phase. Witha positioning of the flame below the refractory line, there issubstantially less possibility for a flash back and the refractory canwithstand such operation without catastrophic failure. The process ofmelting a clear path is also faster because the flame works in a hotterarea closer to the electric arc. Further, the hot combustion gases flowupward through the total burden of scrap and cause additional energytransfer instead of heating the furnace atmosphere. For steel makingprocesses in which there is no scrap path to melt, the earlyintroduction of the flame is more efficient because of the deceased pathlength to the iron carbon melt.

In addition to the efficiency gain caused by starting the oxidizing gasand particulate flows early in the steel making cycle, the inventionincludes a process for increasing the efficiency of the oxidizing gasutilization in the iron carbon melt and includes a process forincreasing the efficiency of the particulate carbon utilization in theslag. More particularly, the method preferably includes supplying aplurality of oxidation reaction zones with an oxidizing gas todecarburize an iron carbon melt with an efficient oxygen supply profilewhich is related to the carbon content of the melt. The multipleoxidation reaction zones are used to increase the amount of oxygen whichcan be effectively used for decarburization of the melt by increasingthe reaction zone area and by making each oxidation reaction zone moreefficient. Each oxidation reaction zone is more efficient because thesurface dynamics of the process are occurring in multiple localizedareas. The carbon being depleted in each local area is replenished morequickly than a single large area because of the better mass transport.This will lower the duration the decarburization process and at the sametime oxidize less iron. The method includes supplying a plurality ofparticulate reaction zones with particulate carbon for foaming slag, thereduction of FeO in the slag and/or the recarburization of the ironcarbon melt. The multiple particulate reaction zones are used toincrease the amount of particulate carbon which can be effectively usedfor foaming slag, the reduction of FeO in the slag and/or therecarburization of the iron carbon melt by increasing the reaction zonearea and by making each particulate reaction zone more efficient. Eachparticulate reaction zone is more efficient because the surface dynamicsof the process are occurring in multiple localized areas.

A preferred embodiment of the apparatus includes a plurality ofinjection apparatus which efficiently supply combustion gases, highvelocity oxidizing gas, and high velocity particulates to the respectivereaction zones. The injection apparatus preferably comprises a fixedburner/lance which is capable of injecting combustion gases and highvelocity oxygen, preferably at supersonic velocity, and a particulateinjector capable of injecting at least high velocity carbon particlesentrained in a carrier gas. In the illustrated embodiment, the highvelocity oxygen is developed by a nozzle structure of a burner/lancewhich accelerates the oxidizing gas to supersonic velocity. The nozzlestructure of the burner/lance can also includes fuel and secondaryoxidizing gas jets which are used after combustion to form a shroudaround the high velocity oxygen and maintain its penetrating power overgreater distances.

The burner/lance and particulate injector are mounted in a protectivemounting enclosure which allows the nozzle structure of the burner/lanceand the discharge end of the particulate injector to be located closerto the surface of the melt and closer to the center of the furnace thanprior fixed apparatus mounted on the side wall panels. The protectivemounting enclosure in the preferred embodiment is fluid cooled and hasat least one hot face adapted to withstand the harsh environment of theinside of the furnace. The burner/lance and particulate injector aremounted at an optimal attack angle through mounting apertures in thishot face.

Mounting the burner/lance and particulate injector in a protectivemounting enclosure produces several advantages. The protective enclosuremoves the burner flames, high velocity oxygen flow, and particulate flowaway from the wall of the furnace and closer to the edge of therefractory. This greatly reduces or eliminates the chance that theburner flames or the high velocity oxygen flow will be reflected(flashback) against the furnace wall and create damage. Advantageously,the high velocity oxidizing gas flow and particulate flow have a shorterdistance to travel to reach the melt compared to an apparatus mounted onthe side wall.

The shorter flow path length permits the oxidizing gas flow to impingeon the melt with a higher velocity and more concentrated flow patternwhich causes a more efficient and rapid decarburization. The shorterflow path length also eliminates the need for excessive shrouding gasesand oxygen jets with large flow rates. This significantly reduces thenegative oxidizing effects to the furnace related to excess oxygen. Theshorter flow path length permits the particulate flow to impinge on theslag layer with a higher velocity and more concentrated flow patternwhich causes intensive slag agitation and, as a result, rapid productionof foamy slag and consequent reduction of the FeO in the slag.

Further, the shorter flow path length provided by the mountingenclosures and multiple zones permits reduced flow rates at each zone,allows the flow of the oxidizing gas and particulates at each zone to becontrolled over a substantial range while still maintaining highvelocity and efficient penetrating power for the melt and slag at eachzone. The capability of the preferred apparatus to permit the control ofthe oxidizing gas flow rate over a substantial range while stillmaintaining efficient decarburizing velocity facilitates the supply ofan oxidizing gas profile to each reaction zone which is related to thecarbon content of the melt.

According to another feature of the invention, the apparatus in themounting enclosure provides an oxidizing gas flow, preferably from theburner/lance, and a particulate carbon flow preferably from theparticulate injector, which are substantially parallel and substantiallyat the same injection angle. This is advantageous because the flows donot intersect each other in traveling to the slag and the melt. Theflows impinge on the slag and melt to form separate reaction zones whichessentially move together as the bath level changes. The oxidizing gasflow penetrates the melt to provide effective decarburization in theoxidation reaction zone and the particulate carbon flow penetrates theslag to provide effective reduction of FeO and/or slag foaming in thereaction zone. These effective reaction zones can be established earlyin the steel making process and remain efficient over a wide range oflevels of the bath. Preferably, the zones may be started during themelting phase for a conventional scrap melting EAF or at the beginningof DRI introduction for an EAF which is charged with scrap and/or hotiron and continues to charge DRI from the top. Beginning the effectivereaction zones at the start of the process is beneficial for an EAFusing a ConSteel process where scrap is continuously charged into thebath by different type of conveyers.

According to still another aspect of the invention, the oxidationreaction zone and particulate injection zone are located independentlybut synergistically with respect to each other to facilitate the desiredreactions in each. Preferably, at least one particulate reaction zone islocated on the periphery of an oxidation reaction zone to separate thereactions so they do not substantially interfere with one another.

Each oxidation reaction zone will produce FeO in the slag along with COand heat from the oxidation of carbon in the melt. The amount of FeOproduced in the slag will depend upon the amount of oxygen being used atthe time, temperature, the carbon content of the melt and the percentageof FeO already in the slag. Due to the natural circulation of the slagcaused by the magnetic field of the electrodes (typically counterclockwise in either an AC or DC furnace) there will be an downstreamside of each oxidation reaction zone where slag with high concentrationsof hot FeO will exit the zone. Preferably, an associated particulatereaction zone is located downstream of at least one oxidation reactionzone to recover a part of this FeO and to foam the slag. Another benefitis that the slag is cooled by the endothermic reaction of theparticulate carbon which will increase its viscosity. The increasedviscosity of the slag and production of CO bubbles from the reductionreaction will produce a stable and vigorous foamy slag.

Additionally, the hot FeO in each oxidation reaction zone is reactiveand when it comes into contact with the refractory of the furnace thelife of the refractory is reduced. Preferably, at least one associatedparticulate reaction zone is located between at least one oxidationreaction zone and the furnace refractory to recover a part of the hotFeO before it reaches the refractory. In this situation the endothermicreaction with the particulate carbon and FeO also cools the slag andmakes the remaining FeO and slag less detrimental to the refractory.

Injection apparatus according to the invention can also be used for animproved method for recarburizing an iron carbon melt. The injectionapparatus for this purpose preferably comprises a fixed burner which iscapable of injecting combustion gases and a particulate injector capableof injecting at least high velocity carbon particles entrained in acarrier gas. The burner and particulate injector are mounted in aprotective mounting enclosure which allows the nozzle structure of theburner and the discharge end of the particulate injector to be locatedcloser to the surface of the melt and closer to the center of thefurnace than prior fixed apparatus mounted on the side wall panels. Theprotective mounting enclosure in the preferred embodiment is fluidcooled and has at least one hot face adapted to withstand the harshenvironment of the inside of the furnace. The burner and particulateinjector are mounted at an optimal attack angle through mountingapertures in this hot face.

Multiple injection apparatus which efficiently supply combustion gasesand high velocity carbon particulates to the respective reaction zonesare used in a process to add carbon content to the iron carbon melt. Theflows of combustion gases are applied at the same time or substantiallythe same time as the flows of carbon particulates to increase the carbonlevel of the melt. The separate reactions zones allow the combustiongases to heat the slag to reduce its viscosity without burning thecarbon. The carbon is injected into the thinner slag and can moreefficiently penetrate through to the iron carbon melt. The shorterinjection distance to the melt provided by the mounting enclosurepermits the carbon particles to impinge on the melt with greatervelocity so that they can be incorporated easily therein. The multiplecarbon injection points allow relatively large amounts of carbon to beadded to the iron carbon melt quickly and with a uniform distribution.This shortens the duration of the recarburization process and allows thebath to come to equilibrium in an optimal amount of time.

These and other objects, aspects and features of the invention will bemore clearly understood and better described when the following detaileddescription is read in conjunction with the attached drawings, whereinsimilar elements throughout the views have the same reference numerals,and wherein;

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cross-sectioned side view of a first embodiment aninjection apparatus mounted on an electric arc furnace which is capableof more efficient operation for melting, decarburization of an ironcarbon melt and introduction of particulates and which is constructed inaccordance with the invention;

FIG. 2 is a cross-sectioned side view of the injection apparatusillustrated in FIG. 1 which shows the burner/lance and particulateinjector of the apparatus;

FIG. 3 is a rear view of the injection apparatus illustrated in FIG. 1which shows the mounting enclosure without the burner/lance andparticulate injector of the apparatus;

FIG. 4 is a front view of the injector apparatus illustrated in FIG. 1;

FIG. 5 is a partially cross-sectioned plan view of a multiple injectionapparatus configuration for the electric arc furnace illustrated in FIG.1 illustrating a plurality of the injector apparatus and a flowcontroller for regulation of their operation;

FIG. 6 is a pictorial representation of the reactions occurring in theoxidizing gas reaction zone and the particulate reaction zone for theinjection apparatus shown in FIG. 1;

FIG. 7 is a graphical representation of the chemical energy as afunction of time input by injection apparatus during the first charge ofthe melting phase for the steel making process of the improvedconfiguration illustrated in FIGS. 1-5;

FIG. 8 is a graphical representation of the chemical energy as afunction of time input by injection apparatus during the second chargeof the melting phase and refining phase for the steel making process ofthe improved configuration illustrated in FIGS. 1-5;

FIG. 9 is a graphical representation of the total input of electricalenergy and chemical energy to an electric arc furnace as a function timefor a steel making process according to one aspect of the presentinvention.

FIG. 10 is a cross-sectioned side view of a second embodiment ofinjection apparatus which shows the burner/lance and the two particulateinjectors of the apparatus;

FIG. 11 is a rear view of the injection apparatus illustrated in FIG. 10which shows the mounting enclosure without the burner/lance andparticulate injectors of the apparatus;

FIG. 12 is a front view of the injection apparatus illustrated in FIG.10; and

FIG. 13 is a partially cross-sectioned plan view of the injectionapparatus illustrated in FIGS. 10-12 mounted on an electric arc furnacepictorially representing the oxidation reaction zone and particulatereaction zones.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-5, a plurality of injection apparatus 11 areadapted to operate in several different modes to provide auxiliaryheating, metal refining, particulate injection and other metallurgicalprocessing capabilities for an electric arc furnace (EAF) 15, or similarfurnace for metal melting, refining and processing. The injectionapparatus 11 are capable of providing flows of combustion gases, highvelocity oxidizing gas, and high velocity particulates either singularlyor in any combination.

In an illustrated first embodiment in FIGS. 1-4, the injection apparatus11 preferably includes a burner/lance 10, a particulate injector 13 anda mounting enclosure 14. Preferably, the burner/lances 10 can be thosedescribed previously in the Shver, Shver, et al. I or II references, butthey could also be other commercially available air fuel burners; oxygenfuel burners; oxygen, air and fuel burners; and/or oxygen injectors.Preferably, the particulate injector 13 comprises a hollow pipe throughwhich particulates entrained in a carrier gas, such as carbon particlescarried by pressurized air, can be introduced into the furnace 15.Preferably, the mounting enclosure 14 can be any those disclosed in theincorporated references, U.S. application Ser. Nos. 09/502,064;09/875,153; or 09/902,139. Specifically, additional details as to theconstruction and operation of the injection apparatus 11 of FIGS. 1-4are disclosed in Ser. No. 09/902,139.

While the preferred embodiments of the invention will be described usingand mounting such burner/lances and particulate injectors in thedisclosed mounting enclosures, it will be evident that other similarapparatus, such as consumable, or water cooled fixed lances, retractablelances, or the like, can be used with the invention to produceadvantageous results.

The invention will be useful for any metal melting, refining orprocessing furnace having apparatus with a discharge opening whoseefficiency can be increased by placing the discharge opening closer tothe surface of the molten metal or closer to the center of the furnace.Particularly, the invention will be advantageous for those apparatus,such as burner/lances and lances, which have a lancing capability with ahigh velocity oxidizing gas, such as supersonic oxygen, and for thoseapparatus, such as particulate injectors, which have a injectioncapability with a high velocity particulate flow, for example carbonparticles entrained in a high velocity carrier gas.

FIG. 1 shows a partially sectioned side view of the electric arc furnace15. The EAF 15 melts ferrous scrap, or other iron based materials, bymeans of an electric arc 17 produced from one or more electrodes 20 tocollect a molten metal bath or melt 18 at its hearth 21. The burnerportions of the burner/lances 10 assist in the scrap melting process, oradd heat to other processes, by introducing high temperature flames andcombustion products which transfer heat to the scrap or other burden.The metal bath level varies significantly during the melting process.The bath level generally begins with a hot heel level 29 which is theiron melt left from the previous heat. As multiple charges of scrap orother iron base materials are melted the level rises. The furnace can befilled to a level about 18 inches down from the sill line. Other steelmaking processes such as DRI melting and the ConSteel process producesimilar bath level changes. The generally spherical shaped hearth 21 ismade of refractory material to withstand the high temperature of themolten metal. As best seen in FIG. 5, the hearth 21 of the EAF 15 issurrounded by an upper shell which is comprised of a series of arcuatefluid cooled panels 23. It is known that the fluid cooled panels 23forming the side wall of the furnace 15 can be of several conventionaltypes. These panels are supplied with cooling water from circumferentialsupply conduits 50 and 51 (FIGS. 1-4) which are connected to cause waterto circulate through the panels 23 and then exit to carry off heat. Theinjection apparatus 11 may also be supplied by conduits 50 and 51 orhave independent fluid cooling supplies.

Returning to FIG. 1, the melt 18 consisting of iron and carbon isgenerally covered with various amounts of slag 16 which is produced bythe chemical reactions between the melt and slag forming materials addedto the furnace before or during the melting process of the metal. Oncethe scrap metal or other burden has been melted, the metal bath 18 isgenerally refined and decarburized by oxygen lancing. This produces therequired chemistry for the melt and reduces the carbon content of themetal to the grade of steel desired. After the electrodes are turned on,a foamy slag may be developed by injecting particulate carbon to protectthe furnace components from radiation form the arc. During refining andthereafter, the metal bath 18 is typically heated by the electric arc 17above its melting temperature. This superheating allows the melt to boiland continue the carbon oxidation with the lanced oxygen. Thesuperheating is also used to allow the metal bath 18 to remain fluidwhile being transported in a ladle or other carrier to another processstep. If the melt 18 does not contain an adequate carbon level for thegrade of steel desired then it must be recarburized by adding carbon tothe bath. The melt 18 may lack an adequate carbon level because of thematerials which were melted to form the bath or because oxygen lancinghas decreased the carbon content to below that desired.

The injection apparatus 11 may assist in one or more of these phases ofsteel making. For example, heat may be added at any necessary time bythe burner portion of burner/lance 10 such as for scrap or other burdenmelting. Oxygen lancing for cutting scrap or supersonic oxygen lancingfor decarburization may take place when desired from the lancing portionof the burner/lance 10. The high velocity, preferably supersonic,oxidizing gas lancing may be accompanied by a flame shroud form theburner portion of burner/lance 10 for part or all of its duration. Slagforming particulates or slag foaming, preferably carbon particles,particulates may be injected when desired by the particulate injector13. Recarburization may be accomplished by the particulate injector 13injecting particulate carbon at the desired time with or without theassistance of the burner portion of the burner/lance 10. FIG. 1illustrates that flows of the high velocity oxidizing gas (supersonicjet core) may be accompanied at least part of the time by flows of thecombustion gas (flame envelope) and particulates 25. These flows can beinjected early in the melting process at initial bath levels and as thebath level rises to a full level.

In FIGS. 2-4, the burner/lance 10 and particulate injector 13 arepreferably mounted through an opening in the fluid cooling coils of aside wall panel 23 of the furnace 15 with generally rectangular shapedmounting enclosure 14. In the illustrated embodiment, the mountingenclosure 14 preferably rests on the step 24 formed between the panels23 of the side wall of the upper shell of the furnace 15 and therefractory of the hearth 21, but could also be supported or suspendedfrom another suitable structural member of the furnace 15. To providethermal contact between the mounting enclosure 14, the step 24, andcoils 22, a refractory ramming material 34 is used to close any gaparound the bottom and sides of the enclosure. The mounting enclosure 14is shown located on the inside of the cooling coils 22 of the side wallpanel 23.

The burner/lance 10 is received in a mounting aperture 26 of themounting enclosure 14 so that its discharge opening or face is extendednear the hot edge 12 of the refractory of hearth 21. The burner/lance 10is secured to the mounting enclosure 14 by bolting it to a flange 38.This allows the flow of materials from the discharge opening of theburner/lance 10 to miss the edge of the step so as to not degrade therefractory, particularly with a high velocity oxidizing gas. Themounting of the discharge opening of the burner/lance 10 over the stepalso brings the gas flows from the burner 10 close to the surface of themelt 18 and close to the center of the furnace 15 thereby making theprocess operation more efficient. The mounting enclosure 14 alsoprovides protection for the burner/lance 10 from the intense heat of thefurnace 15 and mechanical damage from falling scrap 13. In normaloperation a slag covering 32 forms on the mounting enclosure 14.

The particulate injector 13 slides into a mounting tube 27 fixed in themounting enclosure 14 so that its discharge opening or face is extendednear the hot edge 12 of the refractory of hearth 21. This allows theflow of materials from the discharge opening of the particulate injector13 to miss the edge of the step and not be dispersed. The mounting ofthe discharge opening of the particulate injector 13 over the step alsobrings the particulate flow close to the surface of the melt 18 andclose to the center of the furnace 15 thereby making the processoperation more efficient. The mounting enclosure 14 also providesprotection for the particulate injector 13 from the intense heat of thefurnace 15 and mechanical damage from falling scrap 13.

The burner/lance 10 is typically slanted downward at a mounting angle inthe mounting aperture 26, preferably between 30-60 degrees, to direct amaterial flow from the burner/lance 10 comprised of combustion products,high velocity oxidizing gas, combinations thereof and/or other flows ofinjected materials, toward the metal melt 18 in the hearth 21 of thefurnace. In addition to its downward inclination, the burner/lance 10may also optionally be directed from a radial direction (center of thefurnace), preferably from 0-15 degrees. To cause suitable penetration ofthe metal bath 18 without splashing, a supersonic flow of oxidizing gas,preferably oxygen, should impinge at an angle which is neither tooshallow nor too steep. If the angle is too steep, excessive steel andslag splashing may occur. If the angle is too shallow, then the flow maynot sufficiently penetrate the surface of the melt 18. More preferably,an angle of approximately 45° (±10°) has been found to be efficacious inproducing desirable results from lancing with combustion products and ahigh velocity oxidizing gas.

The particulate injector 13 is typically slanted downward at a mountingangle in the mounting tube 27, preferably between 30-60 degrees, todirect a material flow from the particulate injector 13 comprised ofvarious slag forming or foaming agents, particulate carbon entrained ina carrier gas, combinations thereof and/or other flows of injectedmaterials, toward the metal melt 18 in the hearth 21 of the furnace 15.In addition to its downward inclination, the particulate injector 13 mayalso optionally be directed from a radial direction (center of thefurnace), preferably from 0-15 degrees. To cause suitable penetration ofthe slag and agitation the flow of particulates should impinge at anangle which is neither too shallow nor too steep. If the angle is toosteep, excessive steel and slag splashing may occur. If the angle is tooshallow, then the flow may not sufficiently penetrate the surface of theslag. More preferably, an angle of approximately 45° (±10°) has beenfound to be efficacious in producing desirable results from highvelocity particulate flows.

Depending upon the configuration of the furnace 15, as seen in the planview in FIG. 5, the injection apparatus 11 may be mounted anywhere alongon the side wall of the upper shell. Individual burners/lances orburners (not shown) may also be mounted in, or above the slag door 28 ofthe furnace 15, and in or above sump 27, if it is an eccentric bottomtapping furnace. Generally, a modern furnace 15 has more than oneinjection apparatus 11 mounted around its periphery; the numberdepending upon its size, configuration, melting power and operation.

Generally, the injection apparatus 11 are strategically located alongthe side wall 23 for a number of different purposes. For example, theinjection apparatus 11 may be mounted at the cold spots in the furnaceso that the burners may assist with the melting of scrap metal. Thesecold spots are different for DC (Direct-Current) furnaces and AC(Alternating Current) furnaces, and may be different even between thesetypes of furnaces depending on size, manufacturer, and the operatingprocedure of the furnace. Positioning may also depend on the specific ofoperation the EAF with different processes, such as scrap melting,continuous charging of DRI, or the ConSteel processes. It may alsodepends on the other factors such as the materials which are introducedinto the furnace by the burner/lance 10 and particulate injector 13 andthe purpose and timing of their introduction. Other materials which canbe introduced include metallurgical and alloying agents, slag formingand foaming agents, oxidizing gases for refining, melting,decarburization agents, post combustion gases, etc. The mountingenclosure 14 of the injection apparatus 11 can be positioned andadvantageously mount a burner/lance 10, particulate injector 13 and/orsimilar apparatus wherever they need to be on the side wall of thefurnace 15 and for a variety of purposes.

In the preferred embodiment, there are four injection apparatus 11 whichare equally spaced around the periphery of the furnace 15. Theconfiguration, according to the invention, is used to provide a uniformdistribution of oxidation reaction zones 52, 54, 56 and 58 fordecarburization and uniform distribution for particulate reaction zones60 for forming and foaming slag, reducing FeO, and recarburization,among other things. The oxidizing gas reaction zones 52, 54, 56 and 58are representations of the areas where the high velocity oxidizing gaspenetrates the slag and iron carbon melt and an oxidizing reaction,termed decarburization, between the lancing gas and the bath carbonoccurs. The particulate reaction zones 60 are where the particulatespenetrate the slag and react chemically with the slag to provide thecorrect viscosity, composition and foaming. By providing a plurality ofreaction zones, the invention not only produces a more uniformdistribution of the oxidizing gas and particulates but also more area inwhich the desired reactions can occur. This allows increased amounts ofeffectively used oxidizing gases where they contribute to reducing thedecarburization time, not to over oxidizing the iron carbon melt orproducing free oxygen in the furnace atmosphere.

One of the oxidizing reaction zones 52 and its associated particulatereaction zone 60 are more detailed in FIG. 6. The injection componentsof the injection apparatus 11 are mounted to direct the flows ofoxidizing gas and particulate carbon in substantially parallel paths.The oxidizing gas flow impinges on the slag and melt at area 52 andpenetrates the slag and melt. Exothermic reactions of oxidation occur todecarburize the melt (2C+O₂=2CO) and to form ferric oxide (2Fe+O₂=2FeO).The heat and FeO remain in the slag, which circulates through the zone52 counter clockwise around the furnace due to the force produced by themagnetic field of the EAF 15. The hot FeO in the slag enters particulatereaction zone 60 by way of furnace circulation because of its downstreamlocation. The particulate carbon flow impinges on the slag and melt atarea 60 and penetrates the slag. A reduction reaction occurs so as torecover a part of the Fe and form CO gas (FeO+C═Fe+CO) which isendothermic. The endothermic reaction helps cool the slag in area 60 toincrease its viscosity thereby assisting in the trapping of the CO gasin bubbles to vigorously foam the slag.

Importantly, because of the parallel direction of the particulate carbonand oxygen flows, one reaction zone does not interfere with the primarychemical reaction in the other zone. The positioning of the (reduction)particulate reaction zone on the downstream side of the oxidationreaction zone enhances the reduction reaction and slag foaming.Moreover, because the flow directions of the carbon and oxygen aresubstantially parallel, the zones will move together as the level of thebath changes (toward the side wall as it increases and away from thesidewall as it decreases) Therefore, the flows will always be focusedtogether. The reaction zone movements are minimized by the highinjection angle allowed by the positioning of the discharge ends of theinjection apparatus 10 and 13 over the step 24. All of the factorscombine in providing stable reaction zones and in improving theeffectiveness of the desired reactions and the steel making process.

Whatever the other functions or modes the burner/lances 10 may have, itis important when an oxidizing gas lancing mode is provided, that theapparatus be closer to the surface of the melt and be directed more tothe center of the furnace. Further, when a multimode burner/lance 10 hasa burner mode which assists in melting scrap and/or clearing a pathwaythrough the scrap for the lancing mode, it is important that theapparatus be closer to the surface of the melt and be directed more tothe center of the furnace. Similarly, the particulate injection isincreased in efficiency when operated closer to the surface of the meltand directed more to the center of the furnace. The mounting enclosure14 provides an extension for mounting the burner/lance 10 andparticulate injector 13 beyond the water cooled panels 23 of the furnace15 to allow their discharge openings to reach beyond the step 24 of therefractory of the hearth 21 and be closer to the center of the furnace.

In the illustrated system embodiment of FIG. 5, the burner/lances 10 arepreferably conventional multimode apparatus which have a burner functionand a lancing function. A burner/lance provides one apparatus for theinjection of thermal energy to assist in the melting phase of the steelmaking process and for the injection of high velocity oxidizing gas todecarburize the iron carbon melt. The burner function of theburner/lances 10 is provided by mixing an oxidizing gas, preferablyoxygen, and fuel, preferably natural gas, which produces a flamecomprised of combustion gases having a high heat content. The thermalenergy of the combustion gases may be transferred to the scrap metalwhich is melted in the furnace through radiation and convection, or acombination of these, as is known.

To control the burner function, a flow controller 40 is used to controlthe flows of oxidizing gas and fuel to each of the burner/lances 10 bymeans of flow control actuators and sensors groups 42, 44, 46, and 48located in the supply paths between the burner/lances 10 and utilities50. The flow controller 40 preferably is a programmable device which hasa program for independently controlling the burner function for eachburner/lance 10 as to at least its oxidizing gas/fuel ratio and itsthermal power output. Preferably, the flow controller 40 additionallycontrols the lancing function of each of the burner/lances 10 throughits program as to the amount (flow) of high velocity oxygen and itstiming. Optionally, the flow controller 40 has as part of its programthe control of a flame for shrouding the high velocity oxidizing gas toincrease its effective penetrating power of the iron carbon melt. Theflow controller 40 also controls the particulate injection of theparticulate injectors 13 through its program with the actuators andsensors as to the amount (flow) of high velocity particulates and theirtiming. Optionally, the flow controller 40 may include as part of itsprogram the receipt of operator commands which control the timing of thestarting and stopping of particulate flow.

The flow controller 40 also receives inputs 53, either manually, fromsensors, from another programmed control (for example, a controllerregulating the electrical energy of the arc) or from an internal timerindicating the phase of the steel making process, carbon content of theiron carbon melt and an indication whether an adequate foamy slag hasbeen established. The flow controller 40 uses these physical parametersof the furnace 15 to determine by its program when the modes of theburner function should be changed, when the burner function should bechanged to the lancing function, and how the lancing function should bevaried.

Conventional mounting configuration for a burner/lance or a particulateinjector has the apparatus mounted in the water cooled side wall panel23 typically located at least 24 inches above the step 24 and about15-24 inches away from the hot face 12 of the refractory 21 (dependingupon the width of the refractory) so that the burner/lance flame andoxidizing gas flow or the particulate flow clears the step 24. A typicalfurnace 15 is shown on FIG. 1, where the My melted steel line comes toabout 18 inches down from the sill line or step 24. The slag line istypically about 8 inches up from the steel line without foaming. With aconventional configuration, the burner/lance and particulate injectormust wait until the steel line advances from the bottom of the furnace,or from the hot heel level 29, to almost fully melted during one orseveral melting stages. Unless the slag and steel lines can bepenetrated by the supersonic jet core, the oxidizing gas lancing willnot be effective and will only contribute to over oxidation of the ironcarbon melt and free oxygen in the furnace atmosphere, both beingdetrimental to the operation of an efficient steel making process. Inaddition, because there is scrap in the way of the oxidizing gas lancingand particulate injection, it must be cleared before such operations canoccur.

The configuration for the burner/lance 10, particulate injector 13 andenclosure 14 in FIGS. 1-5 illustrate that effective lancing with theoxidizing gas and particulate addition can be made much earlier in themelting cycle. The discharge ends of the burner/lance 10 and particulateinjector 13 have been advanced to the edge of the hot face 12 of therefractory by protecting the apparatus with the enclosure 14. This movesthe face or discharge ends of the burner/lance 10 and particulateinjector 13 down (toward the melt) by the distance that the side wallburner has to be elevated to fire over the step and in (toward thecenter of the furnace) by the width of the step. This produces severaladvantages in operation over the conventional configuration. For theburner function, there is a much shorter distance to clear a paththrough the scrap to the surface of the melt so that this task can occurfaster. In addition, the burner flame with this positioning can notflash back into the water cooled panel 23 and, if some flash backoccurs, it will be absorbed by the refractory 21 which will not failunder such operation. Therefore, the burner function of the burner/lance10 may be turned to its maximum rating much earlier than a conventionalburner/lance. The thermal energy from the burner/lance is used moreefficiently than before because, instead of bouncing off the outside ofthe scrap burden 13, the hot gases permeate through it therebytransferring more energy to the scrap.

With respect to the lancing function of the burner/lance 10, thedistance that the flow of oxidizing gas must travel from the dischargeend of the apparatus to the slag and melt surface has also been reducedby an amount proportional to the distance it was moved down and closerto the center. This alone produces a significant increase indecarburization efficiency. In FIG. 1, once a path has been cleared, itis shown that this allows the oxidizing gas to reach a semi-molten steellevel with effective lancing power much earlier in the melting cyclethan a conventional configuration, even with the same burner/lance. Thispermits effective decarburization to begin earlier in the melting cycleso that it may be completed earlier and reduce overall process time.Further, after the start of effective lancing the scrap continues tomelt and the steel line rises to the fully melted stage. From thesemi-melted stage to the fully melted stage and thereafter, the lancingeffectiveness is greater for the burner/lance 10. The supersonic jetcore penetrates deeper into the iron carbon melt because of the reducedpath distance to the melt provided by this configuration.

While the preferred configuration of the burner/lance 10 and particulateinjector 13 mounts their discharge ends as close to the hot face 12 ofthe refractory 21 and sill line 24 as possible to maximize theadvantages of the invention, it is evident that any movement of thedischarge ends in those directions would be beneficial. The advantagesaccrue nonlinearly with the most increase in effectiveness occurringnearer to the sill line and hot face of the refractory, but there isstill a measurable benefit from as small as a 20% movement either towardthe sill line or toward the hot face of the refractory. In other words,the benefits of the invention are obtained from the sill line to 80% ofthe vertical distance between the sill line and a conventional mountingon the side wall and from the hot face to 80% of the horizontal distancebetween the hot face and a conventional mounting on the side wall.

To illustrate the manner in which the invention improves a steel makingprocess, a melting phase, decarburizing and refining phase for steelmaking will now be described with reference to FIGS. 7-9. In FIG. 7multiple modes are scheduled for the burner/lance 10 of the electric arcfurnace 15 during at least one portion of the melting process of thefurnace, in the example, the first of several scrap buckets (firstcharge). This portion of the melting process is scheduled forapproximately 15 min. The burner/lance 10 used in the illustration israted for a maximum output of 5.0 MW. Initially, the burner/lance 10 isoperated in a burner mode at a firing rate of 4.0 MW to make sure it isnot clogged during the loading of the scrap. As soon as the electric arcis turned on for the furnace 15, signaling that the roof is closed andscrap loading is completed, the burner is turned down to 2.0 MW for thefirst 3 minutes of the this portion of the melting cycle. This is toallow the burner/lance 10 to make a pocket in the scrap so that theflame may spread out. During this time for some part of the interval,for example at the start of minute 2 and for approximately 45-60seconds, the oxygen/fuel ratio of the burner is turned up from thestoichiometric ratio (2:1) to a higher ratio of (4:1). This operation,sometimes termed soft lancing because the burner/lance 10 uses subsonicoxygen, allows the scrap to be burned by the excess oxygen so that apocket can be established more readily, clearing the face of theburner/lance 10. Because this soft lancing is directed to impinge on thescrap still remaining in front of the burner and does not reach thereaction zone, it does not effect any decarburization of the melt. Afterabout 3 minutes of operation, the pocket is basically formed and theburner/lance 10 may then be turned up to its maximum rating of 5 MWwhere it is operated from minutes 3-7.5 because it must to preheat thescrap and also clear a path between the front of the burner/lance 10 tothe iron carbon melt which is forming in the furnace 15. After theburner/lance 10 has been on its maximum rating for enough time to assistin melting the scrap, it begins a supersonic oxygen lancing mode for thelast minutes of the melting cycle where effective oxygen can bedelivered to the iron carbon melt in a reaction zone.

Because of the mounting location of the burner/lance 10, the flame doesnot need to melt as long a path through to the iron carbon melt and cando so quickly as compared to a side wall mounted burner/lance. Becauseof its position of firing below the step in the refractory, theburner/lance 10 may be turned on to its maximum rating sooner in themelting cycle of the furnace 15 without concerns of a flashback.Further, the burner/lance 10 melts the scrap faster because the flame isalready located in a spot which is relatively hot from the applicationof the electric arc. In addition, the hot combustion gases rise throughthe rest of the unmelted scrap to transfer their heat content to it.

Supersonic oxygen is started very early in the melting cycle at minute7.5 and continues to the completion of the cycle. The oxygen injectionaccording to the invention can be started at this part of the meltingcycle because of the decreased time of the flame in preparing the pathfor the injection. Because the iron carbon melt is closer to theburner/lance 10, not as much scrap has to be melted before an effectiveoxygen flow can be introduced. Particulate carbon is started very earlyin the melting cycle at minute 11.5 and continues to the completion ofthe cycle. Because a path has been cleared to the slag accumulating inthe furnace hearth, the establishment of a foamy slag for the protectionof the furnace components from arc radiation can be initiated early inthe first or subsequent melting cycles. While the flow of particulatecarbon could be initiated even earlier (as soon as a path has beencleared at minute 7.5 and prior to or with the oxygen lancing), it ispreferred that the oxidation reaction zones be established for severalminutes before particulate carbon is added.

If a second bucket of scrap metal is to be melted, the processidentically shown in FIG. 7 is repeated until all intermediate scrapbuckets have been melted. On the last bucket of scrap to be melted, thesupersonic oxygen is continued throughout a refining phase until theamount of carbon in the iron carbon melt has been reduced to the desiredlevel. Similarly to the particulate injection for the first andintermediate melting stages, The carbon flow are initiated after theoxidation reaction zones are established at minute 8.5 and continuethrough the final melting stage to minute 13. When the refining stagebegins, a vigorous foamy slag has been established and the particulatecarbon flow may be reduced to maintain the foamy slag during therefining phase minutes 13-17.

This process is preferably carried out for two or more burner/lances 10and/or two or more particulate injectors 13, each having an independentreaction zone but which can be controlled together as a system bycontroller 40, As will be more fully discussed hereinafter, once thecarbon content of the iron carbon melt falls below the critical contentamount, approximately 0.15%-0.20% carbon, then the total supersonicoxygen flow for the combined area of the reaction zones is reduced by anamount related to the carbon content.

In FIG. 9, the electrical energy input, chemical energy, lancing ofoxidizing gas and particulate carbon injection for a two charge melting,decarburizing and refining process used in steel making is shown. Duringthe first portion of the melting cycle, the electric arc supplieselectrical energy to the scrap and is aided in the melting process bythe chemical energy from the combustion products of one or moreburner/lances 10. The first bucket of the melting phase is split into atime when the burner/lance 10 supplies a flame and a time when it lanceswith an oxidizing gas. Similarly, a second bucket of scrap is melted bythe electric arc and with the assistance of the combustion products ofone or more burner/lances 10. After the melting cycle, the electric arcpower is reduced and a refining and/or decarburization phase is entered.The second bucket of the melting phase is split into a time when theburner/lance 10 supplies a flame and a time when it supplies lancingwith an oxidizing gas. The initiation of the lancing is limited to aftera path to the iron carbon melt has been cleared and the iron carbon meltis sufficiently established such that effective lancing can take place.Once the second bucket of scrap is melted, the refining decarburizationphase is entered. The lancing of oxidizing gas remains active until thedesired carbon content for the product being made is reached. Thelancing of the oxidizing gas is essentially a time dependent operationwhere a sufficient amount of oxygen must be input to chemically oxidizethe amount of carbon to be removed from the iron carbon melt.

FIG. 9 illustrates one embodiment of the present invention where for thesame furnace and scrap burden, the lancing of the oxidizing gasparticulate carbon injection can be initiated sooner in each of the twomelting phases. While the conventional or side wall mounted burner/lancewas able to start the oxidizing gas lancing at about 80% of the timethrough the each bucket of the melting phase, the present invention canbegin lancing the oxidizing gas much sooner, at approximately 50% of thetime through the each melting phase.

In a preferred embodiment in FIG. 5, for the purpose of decarburization,four separate oxygen reaction zones have been established. The number ofthe multiple zones and their placement are usually suggested by theparticular operation of the furnace and its configuration. Generally,increasing the number of reactions zones increases the total area overwhich the decarburization reaction takes place and is desirable for bothphases of decarburization. Increasing the number of reaction zones makesthe first phase of the decarburization process more efficient byincreasing the amount of oxidizing gas which can be supplied while thereis an excess demand for oxygen. This reduces the time necessary to reachthe critical carbon content of the melt and begin the second phase.Increasing the number of the reaction zones particularly increases theefficiency of the second phase of decarburization where the process isdependent upon the surface kinetics of the process, particularly themass transfer rate of the carbon. In typical furnaces of either the ACtype furnace or the DC type furnace, the number of reaction zones wouldbe a number from 2-8 independent reaction zones.

Normally the steel making process is characterized by a decarburizationprocess in which the amount of carbon in the bath is steadily reduced byblowing oxygen into an iron carbon melt. The rate at which this can bedone is the decarburization rate (−dC/dt) which is measured inpoints/mm, where a point is 0.01%. The decarburization rate is generallyflat until the critical carbon content, approximately 0.15%-0.20% ofcarbon, is reached and then decreases relatively quickly as the carboncontent and reaction kinetics become rate limiting.

The preferred method for controlling the oxygen profile supplied duringa decarburization process will now be disclosed. The flow controller 40includes a program which controls the total amount of oxygen suppliedfrom the four burner/lances 10 during the lancing operation. Thepreferred oxygen profile which the controller applies is based upon theamount of carbon content of the iron carbon melt. The oxygen profile isgenerally split into two sections having: the first section supplying apredetermined amount of oxygen per unit time based upon the rate atwhich the decarburization is to take place, the amount of carbon to beremoved and the time allowed for removing it, generally at about therate of 3-6 points per minute until the critical carbon content isreached; and the second section in which the total oxygen supplied isreduced proportionally to the reduced carbon content to minimize anyover oxidation of the iron carbon melt and free oxygen in the furnaceatmosphere.

Several methods for the oxygen profiling for the second section may beused by the controller 40. The controller 40 can reduce the total oxygensupplied to the multiple reaction zones after the critical carboncontent is reached by (a) turning off one or more of the burner/lances;(b) varying the duty cycle of one or more of the burner/lances; (c) acombination of turning off or varying the duty cycle of one or more ofthe burner/lances; (d) varying the flow rate of one or more of theburner/lances; or (e) by a combination of turning off; varying the flowrate or varying the duty cycle of one or more of the burner/lances.

FIGS. 10-12 illustrate a second preferred embodiment of the injectionapparatus 11. The injection apparatus 11 is similar to the firstembodiment in that it comprises a burner/lance 10, a particulateinjector 13 and a mounting enclosure 14. These elements are constructedand operate in the same manner as described for the similarly numberedelements of the previous embodiment. In this embodiment, a secondparticulate injector 9, similar in construction and operation toinjector 13, has been mounted in the enclosure 14. The mounting positionof the discharge end of the particulate injector 9 is below and to theleft (as looking into the furnace 15 in FIG. 13) of the discharge end ofthe burner/lance 10. The mounting angle of the particulate injector 9 ispreferably approximately 45 degrees, similar to the mounting angle ofthe particulate injector 13 and burner/lance 10. The flows for bothparticulate injectors 9, 13 are substantially parallel to the flow ofoxidizing gas for the burner/lance 10.

With reference now to FIG. 13, the positioning of the second particulateinjector 9 produces a flow of particulates, preferably carbon particlesentrained in a carrier gas, that penetrate the slag at a secondparticulate reaction zone 61. The second particulate reaction zone 61 isalong the periphery of the oxidation reaction zone 52 on its upstreamside so that the normal counterclockwise furnace circulation brings slagwith FeO into the zone. The second particulate reaction zone 61 ispositioned to efficaciously introduce carbon particles between theoxidation reaction zone 52 and the refractory of the furnace above themetal line. The endothermic reaction of the carbon with the slagproduces a cooling effect for the refractory and importantly prevents asubstantial portion of the hot FeO that is being generated in theoxidation reaction zone 52 from reaching the refractory around themounting enclosure 14. This effect combines with the cooling effectproduced by the circulation of fluid through the mounting enclosure incontact with the refractory to prevent erosion of the refractory at theslag/metal interface level.

While the second embodiment illustrates a particular distribution forthe particulate injectors 9 and 13, it is evident that many otherdifferent distributions can be envisioned within the scope of theinvention. One or more particulate injectors may be mounted in theenclosure 14 at various places to produce a flow of particulatematerials establishing one or more particulate reaction zones on theperiphery of the oxidation reaction zone. Those particulate reactionzones established on the downstream side of the oxidation reaction zone52 (to the right of centerline 73) reduce a part of the FeO from theoxidation reaction zone and cool the slag. Those particulate reactionzones established between the oxidation reaction zone 52 and therefractory 21 (below centerline 75) reduce a part of the FeO from theoxidation reaction zone 52 and cool the slag before it reaches therefractory. When multiple oxidation reaction zones are used in a system,each oxidation reaction zone may have none, one or more than oneassociated particulate reaction zone located on its periphery.

The first and second embodiments of the injection apparatus can also beoperated in an improved method for recarburizing an iron carbon melt.Returning to FIG. 5, the multiple injection apparatus 11 whichefficiently supply combustion gases and high velocity carbonparticulates to the respective reaction zones are used in a process toadd carbon content to the iron carbon melt. The flows of combustiongases are applied at the same time or substantially the same time as theflows of carbon particulates to increase the carbon level of the melt.

The separate reactions zones allow the combustion gases to heat the slagto reduce its viscosity without burning the carbon. The carbon isinjected into the thinner slag and can more efficiently penetratethrough to the iron carbon melt. The shorter injection distance to themelt provided by the mounting enclosure permits the carbon particles toimpinge on the melt with greater velocity so that they can beincorporated easily therein. The multiple carbon injection points allowrelatively large amounts of carbon to be added to the iron carbon meltquickly and with a uniform distribution. This shortens the duration ofthe recarburization process and allows the bath to come to equilibriumin an optimal amount of time.

While the invention has been described in connection with the preferredembodiments, this specification is not intended to limit the scope ofthe invention to the particular forms or methods set forth, but, to thecontrary, it is intended to cover any such alternatives, modifications,and equivalents as may be included within the spirit and scope of theinvention as defined by the appended claims.

1. A method of metal melting, refining or processing for an iron carbonmelt, comprising the following steps: A. forming a plurality ofparticulate reaction zones for the iron carbon melt; and B. injecting ahigh velocity flow of particulates entrained in a carrier gas towardeach of said reaction zones from an apparatus having a discharge endmounted near the intersection of the sill line and the hot face of therefractory of the furnace: